Hierarchical organization is a fundamental structure in real-world society, where authority and responsibility are delegated from managers to subordinates. The VIRGO network (Virtual Hierarchical Overlay Network for scalable grid computing) provides a scalable overlay for organizing distributed systems but lacks intrinsic security and privacy mechanisms. This paper proposes Private Virtual Tree Networks (PVTNs), a cryptographically enforced extension that leverages the VIRGO overlay to mirror real organizational hierarchies. In PVTNs, join requests are encrypted with the manager's public key to ensure confidentiality, while membership authorization is enforced through manager-signed delegation certificates. Public keys are treated as organizational secrets and are disclosed only within direct manager-member relationships, resulting in a private, non-enumerable virtual tree. Our work demonstrates, through the system model, protocols, security analysis, and design rationale, that PVTNs achieve scalability, dynamic management, and strong security guarantees without relying on global public key infrastructures.
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